Local firm had wired a small metalclad board via a SWA cable from the Merlin panel at the intake, probably 3 years ago, to provide visitor's toilets.
PHS came in to install ozone generators yesterday, btu didn't proceed through lack of earthing; so I got the call......

I was expecting to find another case of SWA jointed into a plastic box mid-run (twice last year!!) but no, run intact.

Eventually traced to the paint on the merlin gerin DB being so thick that the edges of the gland's locknut hadn't cut through it, the banjo bolt had only flat washers and must have been sat bang in the middle of the drilled hole & not touching the casing.

In just about every job we do now with swa the spec says that there must be a serrated washer between the gland plate, or hole and the locknut that the banjo must be connected to the gland plate via a tapped hole, if the gland plate is not thick enough for the tapped hole to allow a bolt to be fully tightened then the banjo must be linked to the earth bar within the enclosure with a 4mm2 min cable and a star washer and nut used to secure the bolt, also these nuts and bolts must be either stainless or brass and protected with denso and of course if the cable is glanded into a plastic type box the the banjo must be linked to a suitable earth,,,,,,,etc..

The problem is that really after you drill a hole for the swa gland, the hole should be de-burred and then painted to prevent rusting, etc. gone are the days of just scraping off some paint to get continuity between the gland and gland plate

Where the earthing bolt goes through the pre-drilled hole, the serrated washers weren't sharp enough to remove the paint. Found it on testing but took a while to work out why (or where) we had lost the earth.

Cordless grinder had the desired effect to ensure metal to metal contact.

Connect a bit of g/y 4.00 sw.mm from banjo to the earth bar and there is no problem. Also I have about 200 serated washers in stock. Can't remember how I got them, there bicc, so everything on my jobs gets one!